Firefighters at the Sellafield nuclear site are to go on strike for the first time after talks over pay broke down, the GMB union said.
Union members voted to walk out for several 24-hour periods in a dispute over pay grading. It says many firefighters at the plant are performing roles above what they are paid to do, such as paramedic work.
Chris Jukes, GMB senior organiser, said they had attempted to negotiate for several years and had only opted to strike as a "last resort".
A date for the first strike will be set next week. However, union leaders say they were happy to return to the table with Sellafield management for more talks.
Workers at the Sellafield nuclear site in Cumbria have voted to take industrial action in a row over health and safety, said the Unite union.
Unite said its 1,200 members at the site in Cumbria overwhelmingly backed a campaign of action.
A meeting will be held next week to decide what form the action will take.
Unite said it had been trying for 10 months to have a union official appointed to a health and safety role at Sellafield, adding that talks have now broken down.
The cost of decommissioning and cleaning up the nuclear site at Sellafield has increased by £5 billion to £53 billion, the National Audit Office has said.
Private consortium Nuclear Management Partners is to be stripped of a multibillion-pound contract to clean up the nuclear waste site at Sellafield, the Government has confirmed.
The £9 billion contract will switch to the Nuclear Decommissioning Authority.
Nuclear Management Partners, comprised of US engineering group URS, British firm AMEC and French energy firm AREVA, has run the site for more than six years, and was granted a five-year extension in 2013, despite criticism from unions of its performance.
Energy and Climate Change Secretary Ed Davey said: "Sellafield is the biggest and most complex nuclear site in Europe, so it's right that we keep the way it's being managed under constant review.
"We have seen great examples of how this approach can work with Crossrail and the Olympics - and I'm confident we'll see similar results at Sellafield."
Challenges of cleaning up waste at a Cumbria nuclear site are "unprecedented" and more complex than "any other operational or decommissioning nuclear site in the world", the head of the team overseeing Sellafield nuclear site.
NMP chairman Tom Zarges dodged claims costs were spiralling out of control and said the consortium was focused on building on "our experience of the last five years".
The consortium overseeing the clean up of waste at Sellafield nuclear site has failed to meet taxpayer demand and the National Audit Office should review the management of the site, MPs have said.
The American-led management were accused of failing to train and keep staff to the detriment of the project, as well as planning a future for the site which "doesn't make sense".
The cost of cleaning up nuclear waste at Sellafield has soared to "astonishing" levels, with latest figures estimating the bill has already hit £70bn, according to a group of influential MPs.
The Public Accounts Committee (PAC) said the cost would continue to rise and blasted "poor" progress at the Cumbria site.
They also accused Nuclear Management Partners (NMP), who were brought in to manage the clean up, of letting timescales slip and running a project with "escalating" costs.
Among a series of recommendations MPs called on the Nuclear Decommissioning Authority (NDA) to terminate the contract with NMP if their performance did not improve.
The report said the consortium had been brought in six years ago to help Sellafield improve its performance and had its contract extended last October despite "spiralling costs and poor performance".
The World Nuclear Association, which promotes civil nuclear energy, reports that Sellafield has put the elevated radioactivity reading down to "variations in natural background".
Irish officials have been in contact with Britain over raised levels of radioactivity at the Sellafield nuclear reprocessing plant, the government has said.
Only around 112 miles (180km) separates the nuclear site from the coast of Ireland.
"Officials from the Department of the Environment have been in contact with their UK counterparts ... and will receive updates throughout the day," the Irish government said in a statement.